Add a WTForms-compatible textbox macro

This macro:
- accepts a WTForm form field as a parameter
- renders a form field which follows the GOV.UK Elements patterns, both visually
  and in markup terms

It then changes any page which uses either:
- the old, non-WTForms macro or
- the old, WTFforms `render_field` macro

…to use this new macro and removes both of the old ones.

It also adds the option to display hint text above the textbox.

app/main/forms.py

@@ -1,5 +1,5 @@
 from flask_wtf import Form
-from wtforms import StringField, PasswordField, ValidationError
+from wtforms import StringField, PasswordField, ValidationError, TextAreaField
 from wtforms.validators import DataRequired, Email, Length, Regexp
 from app.main.validators import Blacklist, ValidateUserCodes
 
@@ -121,6 +121,19 @@ class AddServiceForm(Form):
             raise ValidationError('Service name already exists')
 
 
+class ServiceNameForm(Form):
+    service_name = StringField(u'New name')
+
+
+class ConfirmPasswordForm(Form):
+    password = PasswordField(u'Enter password')
+
+
+class TemplateForm(Form):
+    template_name = StringField(u'Template name')
+    template_body = TextAreaField(u'Message')
+
+
 class ForgotPasswordForm(Form):
     email_address = email_address()